refactor: unify binding & data provider interfaces

- Removed BindingType enum and all related logic from Binding.
- Made Binding implement new IBinding and IKeyed interfaces.
- Moved node selection logic to IBinding.Select; removed Resolve* methods from Binding.
- Added new IBinding interface for XPath/CssPath selection.
- Refactored IDataProvider to generic IDataProvider<T>; removed GetNode.
- Updated ListContentDataProvider and ParagraphedContentDataProvider to use IBinding.
- Added new ContentsDataProvider, ContentsArrayDataProvider, and DropDownDataProvider for flexible data extraction.
- Updated DataBindings to use IDataProvider<T> properties instead of Binding.
- Updated all usages to new interfaces and patterns.

Beam.Dynamic/IDataProvider.cs

@@ -1,10 +1,14 @@
 using HtmlAgilityPack;
+using System.Text.Json.Serialization;
 
 namespace Beam.Dynamic {
-    [System.Text.Json.Serialization.JsonDerivedType(typeof(ParagraphedContentDataProvider), "paragraphed-data-provider")]
-    [System.Text.Json.Serialization.JsonDerivedType(typeof(ListContentDataProvider), "list-data-provider")]
-    public interface IDataProvider {
-        public string Get(HtmlDocument document);
-        public HtmlNode? GetNode(HtmlDocument document);
+    [JsonDerivedType(typeof(ParagraphedContentDataProvider), "paragraphed")]
+    [JsonDerivedType(typeof(ListContentDataProvider), "list")]
+    [JsonDerivedType(typeof(ContentsArrayDataProvider), "array")]
+    [JsonDerivedType(typeof(ContentsDataProvider), "single")]
+    [JsonDerivedType(typeof(DropDownDataProvider), "dropdown")]
+    public interface IDataProvider<T> {
+        public T Get(HtmlDocument document);
+        //public HtmlNode? GetNode(HtmlDocument document);
     }
 }